In the case of radio systems, particularly in the case of wire-free communication systems, which allow frequency spreading by transmission of data on different transmission channels (for example frequency hopping in the case of Bluetooth), it is possible to mask out specific transmission channels in order in this way to avoid interference influences on the transmission. In the case of the so-called adaptive frequency hopping method (AFH), the masking out of the transmission channels is automatic and matched to the frequency channel.
In general, a distinction is drawn between two approaches for such classification and qualification of a frequency channel, and one of these two approaches is selected for masking out a frequency channel. In a first approach, the connection (for example Bluetooth) to be adapted is changed such that there is no interference with a further connection (for example WLAN=Wireless Local Area Network). In the second approach, the procedure is for the connection (for example Bluetooth) to be adapted to be changed such that any possible interference from another connection has as little interference influence as possible. In this second approach, for example, an assessment of the bit or data packet error rate on the channels may be used for this purpose. In the first approach described above, the field strength can be determined at times at which the connection to be adapted is not active, in order in this way to obtain information about the activity and the use of the transmission channel by another radio system.
The data packet type which is used in radio systems, in particular in wire-free communication systems such as Bluetooth, DECT, etc., and thus also the maximum length of the data packets are dependent on the given and instantaneous operating conditions, as well as on the settings of a host system. These are governed inter alia by the current number of open connections, the presence of speech channels etc. The settings of the host system and the operating conditions may vary and therefore do not always exist in such a way that data packets with the maximum overall length can always be received. It is thus also possible for the length of the data packets to vary within or during a measurement interval that is used for frequency channel classification. This means that an interference component in a frequency channel can be determined only relatively inaccurately, so that the decision to mask out a frequency channel or to use it for data transmission is relatively inaccurate and unreliable.
A method for channel selection and for digital data transmission via a wire-free communication link is known from German Laid-Open Specification DE 101 23 639A1. In this case, two or more channels are provided for data transmission, via which a first and a second transmitting/receiver unit communicate without the use of wires. The digital data communication via a wire-free communication link is provided by means of data packets that are transmitted sequentially via two or more frequency channels. The communication quality of each frequency channel is recorded, and is compared with a quality criterion that can be predetermined. Channels with an inadequate communication quality are replaced by previously unused channels, and/or the set of control data which is contained in each data packet is selected as a function of the recorded overall quality of the communication link. In the case of the methods that are used in a cordless telephone system, only one general quality figure is determined for one frequency channel, and is compared with a quality criterion. The decision as to whether a frequency channel is thus used for data transmission or is masked out can thus be made only very inadequately and with little confidence. Furthermore, in this known method, one or more transmission channels is or are selected first of all, and only after this is the data packet type with which the corresponding data will be transmitted selected. No information about data packet structures and data packet characteristics is thus used in the quality figure for a frequency channel. Thus, with these known methods, the interference component on a frequency channel and whether the frequency channel is identified and classified as an interference source can be determined only very unsatisfactorily.